The rotational spectrum of the p-fluorotoluene-argon van der Waals complex

The microwave rotational spectrum of the p-fluorotoluene-argon van der Waal s complex was analyzed with a molecular beam Fourier transform microwave sp ectrometer. In the frequency splitting of molecular transitions caused by t he internal rotation of the methyl group with respect to the aromatic ring is contained the structure and barrier information. Elucidation is reduced by the analysis of internal rotors direction with respect to the principal axis system of the complex the number of possible solutions in the structur e. An r(s) and r(0) structure of the complex was calculated from these data . The argon is located 3.541(1) Angstrom, above the aromatic ring. By formi ng the complex, the barrier height of internal rotation is changed. An addi tional V-3 term in the potential function occurs in the complex because the molecular symmetry of the p-fluorotoluene, containing a V-6 but no V-3 ter m, is reduced by the argon. For assumed V-6 = 144.79(19) GHz or 57.777(76) J/mol, V-3 is found to equal 552.0(10) GHz or 220.31(40) J/mol. (C) 1999 Ac ademic Press.